The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Environmentally-friendly technology for vehicles is important in the automobile industry, and advanced car makers have focused their energy on the development of an environmentally-friendly vehicle to achieve environmental and fuel efficiency regulations.
Therefore, car makers have developed an electric vehicle (EV), a hybrid electric vehicle (HEV), a fuel cell electric vehicle (FCEV), and the like, as environmentally-friendly vehicle technologies.
Since all vehicles have various technological restrictions such as a weight and cost, the vehicle makers have paid attention to the hybrid electric vehicle as an alternative for meeting exhaust gas regulations and improving fuel efficiency performance and have entered into keen competition for commercializing the hybrid electric vehicle.
The hybrid electric vehicle is a vehicle using two or more power sources. Two or more power sources may be combined by various schemes and a gasoline engine or a diesel engine using the existing fossil fuel and a motor/generator driven by electric energy are mixed and used as the power sources.
The hybrid electric vehicle generally uses an engine and a motor/generator, and uses as a primary power source a motor/generator having a relatively excellent low-speed torque characteristic at a low speed and uses as the primary power source an engine having a relatively excellent high-speed torque characteristic at a high speed.
As a result, the hybrid electric vehicle is useful in fuel efficiency enhancement and reduction of exhaust gas because an operation of the engine using fossil fuel stops and the motor/generator is used at a low-speed section.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.